This invention relates generally to a vortex type flowmeter and more particularly to a vortex flowmeter having a photoelectric, rotor-velocity sensing system and a spoiler system to improve the down side response time of the meter assembly.
A vortex flowmeter generally consists of a confined, generally inverted frustro-conical vortex chamber with a tangential inlet to the vortex chamber and a central outlet. The vortex causes fluid flowing into the chamber to swirl in a generally helical fashion toward the outlet conduit to cause the fluid to increase in velocity as the diameter of the flow path is decreased. Thus, a vortex flowmeter has the tendency to increase the velocity of the fluid through the meter as it is being measured. Typically, a movable unit is provided in the chamber, which unit is acted on by the fluid in the chamber. A measuring system is provided to sense the movement of the movable unit.
In certain prior art flowmeters, it has been proposed to introduce a ball in a raceway within the vortex cavity, which ball is moved along an interior diameter of the vortex cavity by the swirling fluid to be measured. In this system, a magnetic pickup is provided which generally consists of a permanent magnetic and a pickup coil arrangement, which arrangement senses the passage of the ball through the magnetic circuit. As the ball approaches the magnetic circuit, the reluctance of the circuit is decreased, which reduction in reluctance is sensed by the pickup coil. Also, other systems have contemplated the provision of a reed switch pickup arrangement to sense the passage of the ball.
In systems of the type described above, it is seen that the ball provides a single pulse per revolution of the ball within the vortex cavity, which results in a low resolution as only a single revolution of the ball per revolution of fluid is created. Also, magnetic pickups and reed switch pickups create a drag on the ball due to the interaction between the ball and the magnetic circuit in the case of the pickup coil arrangement and the magnetic interaction between the ball and the reed switch in the case of the reed switch arrangement. Thus, serious problems are introduced to the measuring of relatively low flow rates.
Also, in systems such as described above, a problem is introduced in the response time of the meter when the fluid flow is suddenly reduced or cut-off due to the fact that the fluid tends to continue swirling and the ball continues its travel even after the reduction in flow rate has been achieved. Thus, it has been desired to improve the response time on the down side of the flowmeter cycle at high flow rates.
With the system of the present invention, it is contemplated that the interior vortex cavity is provided with a toothed rotor and a light-emitting diode-phototransistor sensing arrangement whereby the passage of each tooth is sensed by the diode-phototransistor sensing system. In the system of the present invention, the rotor is fabricated of a generally unitary structure with a plurality of teeth formed therein, the number of teeth being selected to achieve the desired resolution at low flow rates. Further, the light-emitting diode and phototransistor arrangement is positioned to bridge the gap through which each tooth is passing to sense the passage of each of the rotor teeth. In this way, a large number of pulses per revolution may be generated to achieve resolutions of, for example, twenty-two to twenty-four hertz at a low flow rate of approximately five pounds per hour and nine hundred hertz at a high flow rate of approximately a hundred and fifty pounds per hour. It has been found that an accuracy of approximately a quarter of a percent of the value read may be achieved.
With regard to the problem of improving the response time on the down side of the measuring cycle, the assembly of the present invention includes a spoiler arrangement which generally takes the shape of a spider similar to the rotor utilized in the vortex cavity. This spider is mounted proximate the rotor and parallel thereto, the spider being formed with teeth facing the rotor teeth. With this arrangement, fluid is trapped between the spider teeth to create a static fluid condition. With this static fluid condition, the passage of swirling fluid past the static fluid creates a fluid shear drag condition which tends to cause the rotor to slow down at a faster rate when the fluid has been cut off. Thus, the response time on the down side of the cycle is greatly improved.
Accordingly, it is one object of the present invention to provide an improved vortex flowmeter.
It is another object of the present invention to provide an improved vortex flowmeter having a high resolution relative to prior systems.
It is a further object of the present invention to provide an improved vortex flowmeter having a relatively low drag due to the rotational pickup system.
It is a further object of the present invention to provide an improved vortex flowmeter having a resolution which is as high as is desired consistent with providing the proper interaction between the swirling fluid and the rotational member to be sensed.
It is a further object of the present invention to provide a spoiler arrangement for use in a fluid flowmeter to enhance the down side response time of the flowmeter.
It is still another object of the present invention to provide an improved vortex flowmeter down side response time by providing an assembly for creating a fluid shear drag on the rotating fluid after the source of fluid has been reduced or cut off.